Merge generics and where predicates and prevent duplicates in where predicates

1 files changed, 91 insertions, 33 deletions

diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 80909919ba2..2a2a9470d25 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -12,7 +12,7 @@ pub(crate) mod utils;
 
 use rustc_ast as ast;
 use rustc_attr as attr;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet, IndexEntry};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
@@ -598,47 +598,105 @@ pub(crate) fn clean_generics<'tcx>(
         })
         .collect::<Vec<_>>();
 
+    let mut bound_predicates = FxIndexMap::default();
+    let mut region_predicates = FxIndexMap::default();
+    let mut eq_predicates = ThinVec::default();
+    for pred in gens.predicates.iter().filter_map(|x| clean_where_predicate(x, cx)) {
+        match pred {
+            WherePredicate::BoundPredicate { ty, bounds, bound_params } => {
+                match bound_predicates.entry(ty) {
+                    IndexEntry::Vacant(v) => {
+                        v.insert((bounds, bound_params));
+                    }
+                    IndexEntry::Occupied(mut o) => {
+                        // we merge both bounds.
+                        for bound in bounds {
+                            if !o.get().0.contains(&bound) {
+                                o.get_mut().0.push(bound);
+                            }
+                        }
+                        for bound_param in bound_params {
+                            if !o.get().1.contains(&bound_param) {
+                                o.get_mut().1.push(bound_param);
+                            }
+                        }
+                    }
+                }
+            }
+            WherePredicate::RegionPredicate { lifetime, bounds } => {
+                match region_predicates.entry(lifetime) {
+                    IndexEntry::Vacant(v) => {
+                        v.insert(bounds);
+                    }
+                    IndexEntry::Occupied(mut o) => {
+                        // we merge both bounds.
+                        for bound in bounds {
+                            if !o.get().contains(&bound) {
+                                o.get_mut().push(bound);
+                            }
+                        }
+                    }
+                }
+            }
+            WherePredicate::EqPredicate { lhs, rhs, bound_params } => {
+                eq_predicates.push(WherePredicate::EqPredicate { lhs, rhs, bound_params });
+            }
+        }
+    }
+
     let mut params = ThinVec::with_capacity(gens.params.len());
+    // In this loop, we gather the generic parameters (`<'a, B: 'a>`) and check if they have
+    // bounds in the where predicates. If so, we move their bounds into the where predicates
+    // while also preventing duplicates.
     for p in gens.params.iter().filter(|p| !is_impl_trait(p) && !is_elided_lifetime(p)) {
-        let p = clean_generic_param(cx, Some(gens), p);
+        let mut p = clean_generic_param(cx, Some(gens), p);
+        match &mut p.kind {
+            GenericParamDefKind::Lifetime { ref mut outlives } => {
+                if let Some(region_pred) = region_predicates.get_mut(&Lifetime(p.name)) {
+                    // We merge bounds in the `where` clause.
+                    for outlive in outlives.drain(..) {
+                        let outlive = GenericBound::Outlives(outlive);
+                        if !region_pred.contains(&outlive) {
+                            region_pred.push(outlive);
+                        }
+                    }
+                }
+            }
+            GenericParamDefKind::Type { bounds, synthetic: false, .. } => {
+                if let Some(bound_pred) = bound_predicates.get_mut(&Type::Generic(p.name)) {
+                    // We merge bounds in the `where` clause.
+                    for bound in bounds.drain(..) {
+                        if !bound_pred.0.contains(&bound) {
+                            bound_pred.0.push(bound);
+                        }
+                    }
+                }
+            }
+            GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
+                // nothing to do here.
+            }
+        }
         params.push(p);
     }
     params.extend(impl_trait_params);
 
-    let mut generics = Generics {
+    Generics {
         params,
-        where_predicates: gens
-            .predicates
-            .iter()
-            .filter_map(|x| clean_where_predicate(x, cx))
+        where_predicates: bound_predicates
+            .into_iter()
+            .map(|(ty, (bounds, bound_params))| WherePredicate::BoundPredicate {
+                ty,
+                bounds,
+                bound_params,
+            })
+            .chain(
+                region_predicates
+                    .into_iter()
+                    .map(|(lifetime, bounds)| WherePredicate::RegionPredicate { lifetime, bounds }),
+            )
+            .chain(eq_predicates.into_iter())
             .collect(),
-    };
-
-    // Some duplicates are generated for ?Sized bounds between type params and where
-    // predicates. The point in here is to move the bounds definitions from type params
-    // to where predicates when such cases occur.
-    for where_pred in &mut generics.where_predicates {
-        match *where_pred {
-            WherePredicate::BoundPredicate { ty: Generic(ref name), ref mut bounds, .. } => {
-                if bounds.is_empty() {
-                    for param in &mut generics.params {
-                        match param.kind {
-                            GenericParamDefKind::Lifetime { .. } => {}
-                            GenericParamDefKind::Type { bounds: ref mut ty_bounds, .. } => {
-                                if &param.name == name {
-                                    mem::swap(bounds, ty_bounds);
-                                    break;
-                                }
-                            }
-                            GenericParamDefKind::Const { .. } => {}
-                        }
-                    }
-                }
-            }
-            _ => continue,
-        }
     }
-    generics
 }
 
 fn clean_ty_generics<'tcx>(